RF circuits of transceivers, transmitters and receivers are in demand in today's markets as these devices are used in numerous electronic applications worldwide. RF circuits often provide for mixed-signal systems on a chip and may involve wireless applications for highly integrated system applications. Various architectures are used for transceivers in radio link applications, including a zero-Intermediate frequency (IF) or direct conversion (DC).
FIG. 1 depicts an RF front end circuit comprising an RC filter. From FIG. 1, the RC filter 200 includes a resistor-capacitor circuit 210, a mixer 220, and an amplifier 230. The RC filter 200 is devoid of slicing capability. Input is at 240 and output of the circuit is at 250. RC circuits are often deployed to filter a signal by providing for blocking certain frequencies and passing other frequencies. It will be appreciated by those skilled in the art that RC filters include high-pass filters and low-pass filters.
FIG. 2 depicts a typical topology 300 used in a transmitter for a radio frequency (RF) transceiver or chipset. In FIG. 2, the topology includes a resistor-capacitor (RC) circuit 310 having a voltage source 315, operatively connected with the n mixers (320a-320n) and their respective amplifiers (330a-330n) to provide n switchable amplified split or sliced signal outputs (slice 1 through slice n) that are combined at 340. The combined amplified signals are then provided as input 350 to connected circuitry or devices. The RC circuit 310 may a RC filter or RC network as well where it is minimally an electric circuit composed of resistors and capacitors driven by a voltage or current source. Typically a first order RC circuit is composed of one resistor and one capacitor.
Typically chipsets and transceivers of the topology of FIG. 2, during transmission, output signals typically yield wider bandwidth and show varying gain asymmetry in relation to the slicing. Additionally, when switching between slices, the RC filter may be affected by differing impedance values and therefore affect alternating current (AC) responses. Other aspects of the output may be assessed in terms of any of the following quantifiable characteristics, including:                a. Spectral flatness, a measure of consistency of power density over frequency offset from carrier frequency, often in decibels;        b. Error vector magnitude (EVM) which is understood to be a measure of performance of a digital radio transmitter or receiver reflecting imperfections such as carrier leakage, low image rejection ratio, phase noise etc., causing deviation of the constellation points ideal location points;        c. Adjacent-channel leakage ratio (ACLR) which is understood to be the ratio of the integrated signal power in the adjacent channel to the integrated signal power in the main channel;        d. Long calibration time creating inefficiencies; and,        e. Digital to Analog Converter (DAC) headroom which is understood to be the overhead bit data, other than signal and noise bits, that are needed to prevent overflow.        
Typically, gain symmetry characteristics where there is no RC filter slicing will yield differing shapes of frequency versus peak gain when number of slices at mixers (320a-320n) and their respective amplifiers (330a-330n) changes. Further, amp-frequency plots demonstrate curve changes are affected by band, slicing and R/C values but are generally unaffected by temperature and segments.
It is desired to have an improved slicing method and circuit including the RC filter so it may be driven by a low impedance voltage source which can also provide a more consistent gain step when switching between slices. It is desirable to achieve a consistent AC response over gain setting resulting in less calibration time and complexity, a reasonable DAC headroom, and consistent gain asymmetry shape across all slices. Further desired benefits may also include being able to digitally compensate to flatten the composite transmitter lineup gain over frequency. Therefore, a solution to provide a have an improved slicing method and RC filter circuit capable of being driven by a low impedance voltage source that can also provide a more consistent gain step when switching between slices is desired.
As used herein the terms device, apparatus, system, etc. are intended to be inclusive, interchangeable, and/or synonymous with one another and other similar arrangements and equipment for purposes of the present invention though one will recognize that functionally each may have unique characteristics, functions and/or operations which may be specific to its individual capabilities and/or deployment. It will be appreciated by those skilled in the art that the present invention is applicable to a wide variety of devices, including those associated with communications such as a transmitter, receiver, transceiver and similar devices, all within the scope of the present invention and its various embodiments herein.